Electric-arc lamp.



No. 757,659. PATENTED APR. 19, 1904.

v R. HOPIEELT. ELEGTRIGVARG LAMP.

APPLICATION FILED MAY 18, 1902. N0 MODEL.

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Patented April 19, 1904.

PATENT OFFICE.

ROBERT HOPFELT, OF BERLIN, GERMANY.

ELECTRIC-ARC LAMP.

SPECIFICATION forming part of Letters Patent No. 757,659, dated April 19,1904. Application filed May 13, 1902. Serial No. 107,104. (No model.)

To all whom it may concern.-

Be it known that I, ROBERT HOPFELT, engineer, a subject of the German Emperor, and a resident of 33 Ansbacherstrasse, Berlin, in the German Empire, have invented certain new and useful Improvements in Arc-Lamps; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawing, and to letters of reference marked thereon, which forms a part of this specification.

In the case of electric-arc lamps with electrodes containing metal, which are known to give long electric arcs, it has been shown that their brightness is doubled when the positive metallic electrode is arranged under the negative, so that the metallic vapors can rise to the negative one. In the case of ordinary arclamps, in which the negative electrode is below, such metallic electrodes are not suitable, because by reason of the ascending current of hot air the well-conducting gases attempt to rise at once and do not reach the negative electrode.

If one observes through colored glass an electric arc with the last-named arrangement, it can be seen that only the upper part of the arc is luminous. If, however, the position of the electrodes is reversed, as at first mentioned, so that the vapor-currents can rise from the under electrode to the upper, the entire arc is evenly luminous throughout, and this is the only relative position of vertical metallic electrodes that is practical. In order, however, to avail oneself to advantage of the above-described favorable position, it is necessary to be sure that the metallic vapors can thoroughly traverse the space between the two electrodes. This would not be possible in case only the upper electrode were metallic, because the metallic vapors developed would at once rise without reaching the upper electrode and would not tend, as is desirable, to increase the size of the arc. Besides this the formation of slag on the upper electrode would be greater, and the slag would drop on the lower electrode and disturb the arc. To prevent this difficulty, the lower or positive electrode contains, according to my herein-described invention, at least five per cent. and the upper or negative one less than five per cent. of metal, whereby disturbance of the arc is prevented and increase in its size attained. The elec trodes may contain the metal as such or in the form of its chemical combinations or salts in conjunction with the carbon. In these electrodes the following light-producing additions to the carbon mass may be employed to obtain a long arc: carbid of calcium, oxid of calcium, fluorid of calcium, sulfate of calcium, borate of calcium, or the oxids, sulfates, or borates of magnesium, strontium, or aluminium or the salts of barium. As an addition of pure metal magnesium and aluminium may be mentioned by way of example.

It is advantageous to use in connection with the upper electrode a reflector which will cast the rays downward, as it is in most cases undesirable to allow them to ascend. Also from the electrical standpoint the use of a reflector is advantageous when it is so placed that it touches the are above. It is therefore desirable to so apply the reflector that its plane shall cut the lower surface of the negative electrode. The small amount of annular space between this reflector and the upper carbon tends to draw the rising metallic vapors to the upper carbon, and thus to increase the brightness of the arc, while at the same time greatly steadying this latter, as the ascending vapors are held together and prevent the are from bending or flickering. As in the case of a strong wind or of shaking the arc might from time to time touch the reflector, it is desirable that this latter consist of a material that shall be highly resistant to the action of the arc. All materials that have been hitherto used for this purpose-as soapstone, porcelain, &c. have proved insufficiently durable and have in a short time been destroyed. The only material which has seemed sufficiently refractory in this connection is carbon. Hence I prefer to make my reflector of solid carbon or of a mixture of kaolin or other refractory earths with that material or with carborundum. In addition magnesia, lime, and other refractory materials are suitable for this purpose, and as the metallic vapors cover the carbon electrodes with a white deposit or coating there is here also attained a favorable reflecting effect. Naturally the negative electrode must be electrically insulated from this reflector. The use of this reflector has the further advantage that it serves as an economizer of the upper or negative electrode, so that this latter can be made of smaller cross-section than otherwise would be necessary to attain the same durability.

1n the annexed drawing there is shown an arrangement based on my above-described invention.

All unnecessary details are purposely omitted.

The negative electrode a is placed above the positive one 7). Close above the arc is a re- Hector 0, which surrounds the negative electrode.

Having now particularly described my invention, what 1 claim, and desire to secure by Letters Patent, is

111 an arc-lamp with electrodes partly con1- posed of metal, and in which the negative electrode is above the positive one, and in which thelower or positive electrode contains at least five per cent. and the upper or negative one less than five per cent. of metal for the purpose of lessening the formation of slag on the negative electrode and preventing the dropping 01 slag on the positive one: an annular refractory reflector closely surrounding l the negative electrode, immediately at the are; 

